1. Field of the Invention
The present invention relates to sawing apparatus of a single crystal ingot.
2. Background of the Related Art
Wafers such as silicon are manufactured by slicing a single silicon ingot into slices having a thin thickness. For example, a single crystal ingot is sliced in a wafer form using a predetermined sawing apparatus such as a wire saw while the ingot mounted on a table is moved and slurry is supplied.
However, a distance between a wire and the table is gradually reduced toward a rear end of the ingot to be sliced. As a result, the slurry which is not used during the slicing of the ingot, is supplied into the ingot to be sliced to cause the excessive supply of the slurry. Due to the excessive supply of the slurry, the ingot is over-cooled causing non-uniform shape of a sliced surface of the wafer, thereby deteriorating quality of the wafer.
The slurry (abrasive+oil) also acts as slicing and lubricating agents in the wire saw thereby affecting the quality of the sliced wafer. Although the slurry smeared on a wire acts as the slicing agent for slicing the ingot, scattered slurry or slurry scattered by the wire reciprocated at a high speed may be permeated and accumulated between wafers generated by slicing the ingot to deform a shape of the wafer.
FIG. 1 is a graph illustrating a sliced wrap profile due to slurry supply failure in a related art. FIG. 2 is a nano-map illustrating an example of nano-waviness due to non-uniformly sliced wrap profile.
According to the related art, the slurry scattered when an end (a rear end to be sliced) of the silicon ingot is sliced within the wire saw may have a bad influence on the wafer or straightness of the wire to deform a shape of the end of the wafer. As a result, a flow amount of slurry may be generally reduced at the rear end of the ingot to be sliced. However, when the flow amount of slurry is reduced, a slurry curtain phenomenon (slurry is uniformly spread) may not occur.
Thus, as shown in FIG. 1, the slurry supply failure may occur at a specific portion of the ingot. Therefore, the sliced wrap profile of the wafer may be non-uniform. Also, due to the non-uniform shape of the sliced wrap profile of the wafer, as shown in FIG. 2, waviness pattern errors may occur in a nano-topography process after a polishing process.